The present invention relates to folder superstructures for web printing presses, to nip rolls used in multiribbon transport, as well as to a method for operating a printing press.
In a web printing press, a web or webs may be printed in various printing units. The webs then may enter a folder superstructure. There the webs may be slit into ribbons, which are then superimposed to form a ribbon bundle before passing to a former. The ribbon bundle in the folder superstructure may be drawn over a roller at the top of the former called an RTF by driven nip rolls located after the nose of the former. The ribbon bundle then may pass to folder where the ribbon bundle is cut into signatures.
The nip rolls may be spring-loaded against each other in an adjustable manner so as to set the pressure or “squeeze.” Nip rolls with urethane or rubber outer layers are known. These rubber or urethane coatings are incompressible, as no air, microspheres or other gas inclusions are added to make them compressible.
A ribbon bundle may for example have six ribbons. The draw nip of the nip rolls can create uneven upstream longitudinal tensions of the different ribbons. A small change in nip pressure can also create large ribbon tension changes. To address uneven web tensions, gathering rolls or additional driven pull rolls upstream of the RTF are known.